The present invention relates to a method of measuring/adjusting a relative displacement of objects using diffraction gratings, which can be suitably applied to an exposure apparatus, a pattern evaluating apparatus, and the like for manufacturing, e.g., semiconductor ICs and LSIs.
A method of measuring/adjusting a displacement of an object using a diffraction grating is well known as an effective method of performing mask alignment and setting a gap between the mask and a wafer with high precision. For example, such a method is disclosed in European Patent Publication No. 0151032A2 (Aug. 7, 1985). According to this method, a laser beam is emitted onto diffraction grating marks respectively formed on a wafer and a mask to generate diffracted beams, thereby performing alignment and setting gap in accordance with changes in intensity of the diffracted beams. In this method, a pitch of a wafer-side deviation detecting diffraction grating mark is set to be an integer multiple of that of a mask-side deviation detecting diffraction grating mark, so that a gap variation less adversely affects signals.
However, since an influence of the gap fluctuation cannot be completely eliminated, alignment must be performed at a specific gap value. In addition, during exposure, the mask-side deviation detecting diffraction grating mark is transferred onto the wafer-side deviation detecting diffraction grating mark, the same mark cannot be continuously used in the next process. Therefore, a new wafer-side deviation detecting diffraction grating mark is necessary in each process, and a wide mark updating region is required on the wafer, resulting in a narrow LSI pattern region. Furthermore, since a peak value of an envelope wave of interference waves is searched from a gap detection signal to set a gap, a detector therefor becomes complex, and when a plurality of peak values appear in the envelope wave due to, e.g., multiple interference between the mask and the wafer, a long period of time is required for setting a gap.